Let's start with the standard BCS formulas for the coherence length \(\xi (T, P)\) , and the London penetration depth \(\lambda _{L}(T, P)\)  [1]}, where we include the arguments of pressure \(P = P_{ext} - P_0\)  dependence in the definitions.
\(\xi (T, P) =\frac{\hbar \nu _F}{\pi \Delta },\) 
